JavaScript String indexOf() Method

The JavaScript String indexOf() method finds the index of the first occurrence of the argument string in the given string. The value returned is 0-based.

The indexOf() method is case sensitive.

Syntax:

str.indexOf(searchValue , index);

Parameters:

searchValue: The searchValue is the string that is to be searched in the base string.
index: The index defines the starting index from where the search value is to be searched in the base string.

Return value:

The first position is where the search value occurs. -1 if it never occurs.

Example 1: Below is an example of the String indexOf() Method.

JavaScript

function func() {
 
    // Original string

    let str = 'Departed Train';
 
    // Finding index of occurrence of 'Train'

    let index = str.indexOf('Train');

    console.log(index);
}
func();

Output

Example 2: In this example, the indexOf() method finds the index of the string ed Tr. Since the first and only index where this string is present is 6, therefore this function returns 6 as the answer.

JavaScript

// JavaScript to illustrate indexOf() method

function func() {
 
    // Original string

    let str = 'Departed Train';
 
    // Finding index of occurrence of 'Train'

    let index = str.indexOf('ed Tr');

    console.log(index);
}
func();

Output

Example 3: In this example, the indexOf() method finds the index of the string Train. Since the searchValue is not present in the string, therefore this function returns -1 as the answer.

JavaScript

function func() {
 
    // Original string

    let str = 'Departed Train';
 
    // Finding index of occurrence of 'Train'

    let index = str.indexOf('train');

    console.log(index);
}
func();

Output

-1

Example 4: In this example, the indexOf() method finds the index of the string Train. Since the first index of the searchValue is 9, therefore this function returns 9 as the answer.

JavaScript

function func() {
 
    // Original string

    let str = 'Departed Train before another Train';
 
    // Finding index of occurrence of 'Train'

    let index = str.indexOf('Train');

    console.log(index);
}
func();